1. Field of the Invention
The present invention relates to a level translation circuit that employs a pass switch device used for port isolation, and, more particularly, to level translation circuits that provide a two way path for signals between circuits having different power supply levels.
2. Background Information
Level translators include a pass device, typically and MOS transistor, with its drain defined as one port and its source defined as a second port. Level translation allows information transfer between, for example, a system powered from +3V connected to one port and one powered by +1.8V to the second port.
Known systems were directed to preserving isolation and operability regardless, inter alia, of power supply sequencing, while lowering power dissipation and increasing speed.
One limitation, however, persists. That limitation is that when the power supply to the pass switch is zero or very low, higher potentials at the ports of pass switch may cause an off pass switch to turn on causing a malfunction or improper logic operation of one or both of the circuits connected to the ports or to the pass switch itself.
The term “connected” as used herein means functionally in contact or coupled where passive or other components may be interspersed that do not affect the functionality of the “connection.”
It would be advantageous to ensure that the pass switch off state remains regardless of the voltage at the ports and the power supply for the pass switch itself.